Hammarlund SP-600 JX-16 Restoration Guide

Parameter	Specification
Frequency Coverage	0.54 – 54 MHz in 6 bands
Conversion	Double conversion (above 7 MHz); single below
1st IF	3.955 MHz
2nd IF	455 kHz
Sensitivity (AM)	< 1 µV for 10 dB S+N/N (typical)
Modes	AM · CW · SSB (BFO) · FSK
Tube Complement	~16 tubes (varies by sub-variant)
Power Supply	115/230 VAC, 50/60 Hz
Vintage	c. 1955 – 1969
JX-16 Variant	General-purpose commercial / military version

This guide covers the complete factory-to-operation restoration workflow for the Hammarlund SP-600 JX-16 general-coverage receiver. It addresses component replacement, safety hazards, full RF/IF/BFO alignment, RFI suppression, and transmitter signal purity when the SP-600 is used in a station environment.

1. Electrical Safety — First Priority

The SP-600 operates from mains voltage and contains B+ rails reaching 250–280 VDC. Filter capacitors can hold lethal charge for minutes after power-off. Complete every step in this section before touching internal components.

Hazard	Action Required
Capacitor discharge	After power-off, short B+ to chassis through a 25 kΩ / 5 W bleeder resistor for a minimum of 60 seconds. Use an insulated probe and verify with a meter before touching anything.
Hot chassis / mains	ALWAYS use an isolation transformer rated ≥ 250 VA when servicing. A Variac alone is NOT sufficient protection.
Selenium rectifiers	Original selenium rectifiers can fail open or shorted, emitting toxic selenium dioxide fumes. Replace them before first power-on — no exceptions.
Mains cord	Inspect for cracked insulation, brittle rubber, and correct polarisation. Replace with modern 3-conductor (earth) cord if chassis is not otherwise safely bonded.
Fusing	Verify fuse rating matches the chassis variant. Do not substitute higher-rated fuses. The power transformer has no other short-circuit protection.
HV probe discipline	Never bridge B+ and chassis with bare hands. Use the one-hand-in-pocket rule. Use clip leads and step away before energising.

Recommended Safety Equipment

Item	Purpose	Example / Source
Isolation transformer ≥ 250 VA	Mains isolation	Variac + isolation xfmr or Triad N-68X
Digital multimeter, CAT III rated	Voltage measurement	Fluke 115, Klein MM400
Discharge wand (25 kΩ / 5 W)	B+ bleed-down	DIY or Antique Radio Forums
ESD wrist strap	Solid-state sub-board protection	Any electronics supplier
Safety glasses	Arc / spray protection	Hardware store
Non-conductive work mat	Bench insulation	Rubber anti-static mat

2. Initial Assessment Before Any Power-On

eBay receivers frequently arrive with unknown history, prior amateur modifications, or damaged components. Complete this checklist before applying any power.

• Inspect all tubes — note missing, cracked, or wrong-type substitutions.
• Check for damaged or burned components visible through the chassis top and bottom.
• Test power transformer primary and secondary windings for continuity (no shorts to core).
• Verify selenium rectifiers: replace unconditionally with silicon equivalent (Section 4.3).
• Inspect all electrolytic capacitors for bulging, leakage staining, or split sleeves.
• Check rotary bandswitch wafers for cracked ceramics or burned contacts.
• Inspect the mechanical dial drive and main tuning capacitor for damage or corrosion.
• Verify all shield cans are present — missing cans significantly affect alignment.
• Measure DC resistance across B+ filter caps (should read several kΩ minimum when cold).
• Photograph the chassis top and bottom before disturbing any wiring.

3. Tube Complement — Test, Retain, or Replace

Test every tube on a calibrated emission or mutual-conductance tester. Replace any tube testing below 70% of rated Gm or showing excessive noise or microphonics.

Position / Function	Type	Priority	Notes
RF Amplifier (×2)	6BA6	HIGH	Microphonics critical — select quiet examples
1st Mixer	6BE6	HIGH	Conversion gain directly affects sensitivity
1st Local Oscillator	6C4	HIGH	Frequency stability paramount; test for noise
2nd Mixer	6BE6	HIGH	—
2nd LO / BFO	6C4 or 12AT7	HIGH	Variant-dependent; verify against schematic
1st IF Amp (3.955 MHz)	6BA6	HIGH	—
2nd IF Amp (455 kHz) ×2	6BA6	HIGH	—
AM Detector / AVC	6AL5 or 6H6	MED	Twin diode; test both sections
Audio Driver	12AX7	MED	Test both triode sections
Audio Output	6AQ5 or 6V6	MED	Check for shorts; test output transformer
Noise Limiter	6AL5	LOW	Often 6H6 depending on variant
Rectifier (HV B+)	5Y3GT or 5U4	CRITICAL	Replace selenium alternative unconditionally if fitted
Voltage Regulator	0B2 / 0A2	MED	Gas-filled regulator; test glow stability

4. Capacitor Replacement Schedule

Capacitor failure is the primary cause of dysfunction in receivers of this vintage. The SP-600 uses wax-paper/film coupling and bypass caps throughout the RF and IF chains, plus electrolytic filter caps in the power supply. Replace all categories described below.

4.1 Power Supply Electrolytics

Location	Original Value	Replace With	Notes
Main B+ filter (C1)	40 µF / 350 V	47 µF / 450 V electrolytic	Verify voltage rating physically
Main B+ filter (C2)	40 µF / 350 V	47 µF / 450 V electrolytic	—
Regulated screen supply	20–40 µF / 350 V	47 µF / 450 V	—
Audio B+ bypass	20 µF / 350 V	22 µF / 450 V	—
Bias/AVC filter	25–50 µF / 50 V	47 µF / 63 V	Low-voltage rail
Heater bypass (if present)	100–500 µF / 25 V	Match or increase µF	—

4.2 Wax-Paper / Tubular Coupling & Bypass Capacitors

All wax-paper tubular capacitors — identifiable by brown, yellow, or red wax-coated tubes — must be replaced. They absorb moisture over decades, exhibiting high leakage that shifts bias, loads IF transformers, and kills sensitivity. Use modern 630 V or 1000 V film capacitors (Vishay, Kemet, Wima, or equivalent).

Circuit Area	Typical Values	Replacement Spec	Qty
RF stage coupling / bypass	100 pF – 10 nF	Polypropylene film 630 V	~8
IF transformer coupling	10 nF – 100 nF	Polyester / polypropylene 630 V	~10
AVC / detector bypass	0.01 – 0.1 µF	Polyester film 400 V	~6
Audio coupling	0.01 – 0.05 µF	Polypropylene 400 V	~4
Screen bypass (RF/IF tubes)	0.01 – 0.1 µF	Polyester 400 V	~8
Cathode bypass	1 – 25 µF	Electrolytic or film 100 V	~6
BFO / 2nd LO bypass	100 pF – 1 nF	Silver mica 500 V	~4
Noise limiter / ANL	0.001 – 0.01 µF	Polyester 630 V	~3

4.3 Selenium Rectifier Replacement

Capacitor Vendors

Vendor	Specialty	URL
Digi-Key	Full line; Vishay, Kemet, Wima	digikey.com
Mouser Electronics	Full line; bulk pricing	mouser.com
Antique Electronic Supply	Vintage-value film & electrolytic	tubesandmore.com
Hayseed Hamfest	Authentic vintage-looking replacements	hayseedhamfest.com
Element14 (AU/NZ)	AU-based local stock	au.element14.com
RS Components (AU)	Industrial / pro line; AU shipping	au.rs-online.com

5. Resistors — Inspection & Selective Replacement

Carbon composition resistors drift high with age, often reaching 150–300% of nominal. Measure all resistors in-circuit with power off and one leg lifted. Replace any measuring more than 20% above nominal. Use 1% metal-film replacements (Vishay MRS / Yageo MF series) for best stability.

Circuit Area	Critical Resistors	Why
Oscillator (1st LO, BFO)	Cathode, grid-leak, plate load	Frequency accuracy / drift
AVC time-constant network	AVC filter R-C pairs	Attack/release behaviour
IF amplifier cathode/plate	Cathode resistors	Bias point directly affects gain
Audio output stage	Cathode, screen, plate load	Distortion and output power
Power supply voltage divider	B+ bleeder / regulator chain	All downstream voltages
Noise limiter threshold	Threshold pot + series R	ANL effectiveness

6. Alignment Procedure

Full alignment requires a calibrated signal generator (covering 0.5–55 MHz and the IF frequencies of 3.955 MHz and 455 kHz), an oscilloscope or AC voltmeter, and a frequency counter. Do NOT attempt alignment before completing all component replacements — degraded parts make alignment impossible to hold.

Required Test Equipment

Equipment	Specification	Example
RF Signal Generator	0.1–60 MHz, ±50 ppm or better	R&S SMY, HP 8640B, Heathkit SG-8
Audio / AC Voltmeter	High-Z, 10 mV–10 V, flat to 10 kHz	HP 400D/E, Fluke 8800A
Frequency Counter	≥ 8 digits, 100 MHz range	HP 5315A, any modern TTL counter
Oscilloscope	20 MHz BW minimum	Any vintage or modern scope
Alignment tool set	Non-metallic plastic/phenolic	Core alignment tool kits — AES or eBay

6.1 IF Alignment — 455 kHz (2nd IF)

1. Set the bandswitch to the 80 m band. Disable AVC by grounding the AVC line through a 0.1 µF capacitor to chassis.
2. Inject a 455 kHz signal at approximately 100 µV at the 2nd mixer grid or directly at the 1st 455 kHz IF transformer input.
3. Monitor output on the audio voltmeter. Peak all 455 kHz IF transformer slugs for maximum audio output, working from detector back to 1st IF stage.
4. Reduce signal level as sensitivity increases to avoid overload. Final peak should be achieved at ≤ 10 µV injected.
5. Check IF bandwidth: sweep ±4 kHz either side of 455 kHz — response should be flat (±1 dB) across the passband for AM.
6. If the receiver has crystal filter(s), align the filter termination networks per the schematic — do not adjust the crystal itself.

6.2 IF Alignment — 3.955 MHz (1st IF)

1. Inject a 3.955 MHz signal at the 1st mixer output / 1st IF grid. Monitor at the 2nd mixer input or via the audio meter.
2. Peak all 3.955 MHz IF transformer slugs for maximum transfer to the 2nd IF chain — use small, careful adjustments.
3. Verify centre frequency with the counter on the 2nd mixer injection point (2nd LO should read 3.955 MHz ± 455 kHz).
4. Re-check 455 kHz IF alignment after completing this pass — the two IF stages interact slightly.

6.3 BFO Alignment

1. Set the BFO injection control to mid-range. Measure BFO frequency with the counter at the BFO tube plate or through the coupling capacitor.
2. The BFO should be adjustable to ≥ ±3 kHz either side of 455 kHz for adequate CW/SSB offset coverage.
3. Trim the BFO coil slug until the centre of the BFO control sweep corresponds to ~455.0 kHz.
4. Verify BFO injection level — too high desensitises the receiver; too low produces a weak heterodyne.

6.4 RF & Bandswitch Alignment — All 6 Bands

Work from the highest frequency band down to lowest. Repeat the following for each band:

1. Set the main tuning dial to a calibration frequency near the HIGH end of the band.
2. Inject the corresponding signal at the antenna terminal at ≤ 10 µV.
3. Peak the high-end trimmer capacitor (padder) on the preselector coil for that band.
4. Move to the LOW end of the band. Peak the bandpass coil core (slug) for maximum signal.
5. Iterate between high and low end adjustments until both ends peak simultaneously.
6. Check mid-band tracking — adjust if centre deviates by more than 1–2 kHz.
7. Repeat for all six bands. Verify 1st LO crystal positions with the frequency counter.

6.5 AVC Verification

After completing all IF and RF alignment, reconnect the AVC line. Inject a strong signal (1 mV) at 455 kHz and verify that the AVC voltage develops properly (typically −3 to −8 V on the AVC bus). The AVC should hold audio output roughly constant over a 60 dB input range.

7. RFI Prevention & Shielding

The SP-600’s design predates the modern domestic RFI environment. Without mitigation, switching power supplies, LED drivers, computers, and plasma displays in the same shack will raise the noise floor by 20–40 dB across HF. Implement the following measures.

7.1 Mains Filtering

• Install a quality mains line filter (Schaffner FN9260, Corcom 10ESB10, or equivalent) inline on the SP-600 power cord, as close as possible to the inlet. Minimum 50 dB attenuation at 1 MHz; current rating ≤ 2 A.
• Add X2 / Y2 capacitors: 100 nF X2 across L–N; 4.7 nF Y2 each line-to-earth if not already present in the filter.
• Bond the receiver chassis to station earth ground via a short, heavy (≥ 6 mm²) conductor.

7.2 RF Signal Path

• Use double-shielded coaxial cable (RG-223 or Belden 9913F7) for all antenna feedlines entering the shack.
• Install a coaxial common-mode choke — 12 turns of RG-58 through a Fair-Rite FT-240-31 or FT-240-43 core — at the receiver antenna input to suppress common-mode RFI while passing differential signal RF.
• Verify all shield cans on the SP-600 RF deck are firmly seated and retaining screws tight. Loose cans cause spurious responses and alignment drift.
• Maintain at least 0.5 m physical separation between the antenna lead and switching supplies, LED lamp wiring, and computer peripherals.

7.3 Internal RFI Sources

• If dial lamps have been replaced with LEDs, add a 100 µH inductor in series and 100 nF ceramic caps from each lamp terminal to chassis. Preferably revert to incandescent (6.3 V / 150 mA) for authentic spectrum cleanliness.
• If solid-state modification boards are present, add ferrite bead suppression on all leads and a 100 nF ceramic bypass cap directly across the board’s supply pins.
• Bond all shield-can retaining screws to chassis with conductive paint or star washers to prevent intermittent RF leakage.

Recommended RFI Suppression Components

Item	Specification	Source
Mains line filter	Schaffner FN9260-2-06 or Corcom 10ESB10	Mouser / Digi-Key
CM choke core (HF general)	Fair-Rite FT-240-31	mouser.com, kitsandparts.com
CM choke core (lower HF)	Fair-Rite FT-240-43	mouser.com, kitsandparts.com
Ferrite beads (HF axial)	Fair-Rite 2643480002	Mouser / Digi-Key
X2 capacitors	100 nF 275 VAC X2	Mouser (Kemet, Vishay)
Y2 capacitors	4.7 nF 250 VAC Y2	Mouser (Kemet)
Shielded coax	Belden 9913F7 / RG-223	DX Engineering, Ham Radio Outlet

8. Transmitter Signal Purity — Station Integration

When the SP-600 is used in a two-way station alongside a transmitter, the receiver must be protected from transmit energy, and the transmitter must not be degraded by receiver-side spurious re-radiation. This section covers both directions.

8.1 Receiver Protection from Transmit Energy

• Install a T/R relay or antenna changeover switch rated for the transmitter power level. Ensure contacts switch before RF is applied (QSK keying sequence).
• Add a transmit-mute line to the SP-600 noise blanker/ANL circuit: grounding the mute pin during transmit prevents the receiver front end from saturating.
• Install a low-pass filter on the transmitter output to suppress harmonics before they reach the antenna and re-enter the receiver on image or IF frequencies.
• For high-power stations (> 100 W), add a receive bandpass filter at the SP-600 antenna input to reduce out-of-band transmitter energy.

8.2 Preventing SP-600 LO Radiation

The SP-600’s 1st LO (tuning across 4.5–57.955 MHz) and BFO (near 455 kHz) both radiate weakly through the antenna terminal. In a shared-antenna situation these signals can appear on-band and violate spectral purity requirements.

1. Set the antenna input attenuator to the minimum level consistent with acceptable SNR — this also reduces LO re-radiation.
2. Install a high-isolation T/R changeover relay (50 dB Tx-to-Rx isolation or better) to physically disconnect the receiver antenna port during transmit.
3. Confirm all RF shield cans are seated — loose cans allow LO energy to couple into power wiring or audio leads.
4. In Australia, verify conducted LO emission at the antenna terminal is below −57 dBm per ACMA / ITU-R SM.329 requirements.

8.3 Harmonic & Spurious Suppression Summary

Measure / Control Point	Recommended Limit	Method
Transmitter 2nd harmonic	≥ 43 dB below carrier (< 10 W) or ≥ 50 dB (≥ 10 W)	Low-pass filter at Tx output
Transmitter 3rd / higher harmonics	≥ 50 dB below carrier	Low-pass + notch filter
Transmitter IMD (SSB PEP)	≥ −31 dBc	Linear PA operation; correct ALC setting
Receiver LO at antenna terminal	< −57 dBm (ACMA / ITU)	T/R relay + attenuator
BFO at antenna terminal	< −57 dBm	T/R relay + BFO shielding

9. Restoration Project Plan — Phased Schedule

The following phased plan assumes a receiver in unknown condition from eBay. Adjust phase durations based on findings at each stage. Do not compress phases — rushing alignment after hasty component work is the number-one cause of poor outcomes.

Phase	Tasks	Est. Hours
Phase 1 Documentation & Assessment	Obtain service manual and schematic. Photograph chassis. Visual inspection per Section 2 checklist. Tube inventory and initial test.	3–5 h
Phase 2 Safety Preparation	Install isolation transformer and discharge wand. Inspect/replace mains cord. Replace selenium rectifiers. Verify fuse ratings.	2–3 h
Phase 3 Component Replacement	Replace all electrolytic caps (power supply). Replace all wax-paper tubular caps. Test and replace out-of-tolerance resistors. Replace failed/weak tubes.	8–15 h
Phase 4 Controlled Power-Up	Variac-controlled power-on. Monitor B+ rise and current draw. Measure all supply rails against schematic values. Verify heater voltages.	2–4 h
Phase 5 Functional Check	AM reception test on broadcast band. Verify all bands switch correctly. Check AGC/AVC action. Verify BFO injection. Note any faults.	2–3 h
Phase 6 Alignment	455 kHz IF → 3.955 MHz IF → BFO → RF/bandswitch alignment across all 6 bands → AVC verification.	6–12 h
Phase 7 RFI Mitigation	Install mains line filter. Build and install common-mode choke. Verify LED lamp suppression or revert to incandescent. Check shield can integrity.	3–5 h
Phase 8 Station Integration	Install T/R relay. Configure transmit mute line. Verify transmitter harmonic suppression. Check receiver LO radiation at antenna terminal.	2–4 h
Phase 9 Final Testing & Documentation	Sensitivity measurement (MDS). Selectivity check. IMD/blocking test if equipment available. Document all findings, replaced parts, and final alignment values.	3–5 h

10. Master Parts Vendor Reference

Electronic Components

Vendor	Region	Strength	URL
Digi-Key	Global (AU shipping)	Comprehensive; fast	digikey.com
Mouser Electronics	Global (AU shipping)	Deep stock; bulk	mouser.com
Element14 / Farnell	AU/NZ local stock	AU warehousing	au.element14.com
RS Components	AU local stock	Industrial line	au.rs-online.com
Antique Electronic Supply	US — ships AU	Vintage values / NOS	tubesandmore.com
Hayseed Hamfest	US — ships AU	Authentic repro caps	hayseedhamfest.com
CE Distribution	US — ships AU	Restoration kits	cedist.com

Vacuum Tubes

Vendor	Region	Notes	URL
Antique Electronic Supply	US	Best NOS for SP-600 types	tubesandmore.com
Vacuumtubes.net	US	Tested NOS; 6BA6, 6BE6 stock	vacuumtubes.net
Watford Valves	UK	Good AU shipping; NOS & matched	watfordvalves.com
RF Parts Company	US	RF types; oscillator tubes	rfparts.com
Tube Depot	US	Strong audio / general stock	tubedepot.com

Documentation & Community Resources

Resource	URL / Location
SP-600 Service Manual (PDF)	bama.edebris.com → Hammarlund → SP-600
SP-600 Schematic archive	n4py.com/sp600.htm
Antique Radio Forums (ARF)	antiqueradios.com/forums — dedicated SP-600 threads
Hollow State Newsletter archive	vk6ada.com.au/hollow-state-newsletter
eHam SP-600 reviews / tips	eham.net → Reviews → search SP-600
r-390a.net community	r-390a.net — R-390A / boatanchor community resources

---

Hammarlund SP-600 JX-16 — Complete Restoration Guide
All values are indicative — always verify against the OEM service manual for your specific SP-600 sub-variant.
Mike Peace VK6ADA  ·  r-390a.net Administrator